Porous substrates such as concrete, masonry and wood products are vulnerable to the general effects of weathering and, specifically, to exposure to water and oil. The weathering of concrete substantially shortens the useful life of structures such as highways, bridges, parking ramps, and the like. Exposure of concrete and masonry substrates to water and oil can also significantly shorten the useful life of the product and reduce its aesthetic appeal even before it is no longer functional.
Wood is another product having a porous surface which is used extensively as an interior and exterior construction material for decks, siding, fencing, cedar roofs, walkways, sheds, pedestrian bridges, docks, piers, trellises, log structures, and other wood substrates requiring protection from water, because of its structural integrity, availability, ease of use, and attractive economics. Wood when exposed to water and harsh environmental conditions can deteriorate by a number of mechanisms. For example, wood can deteriorate from ultraviolet light exposure, mildew, splitting, extreme temperatures and temperature changes, water intrusion, etc. Associated with these are customary environmental wet/dry cycles, which cause wood to cyclically swell and contract, causing structural damage.
Water repellent coatings have been formulated for a number of porous substrate materials. Two approaches are commonly taken to obtain water repellency, barrier type materials and highly hydrophobic type materials. Barrier coatings are simply a physical barrier between the environment and the substrate being protected. Common polymeric materials for barrier type waterproofing are vinyl chloride, polyvinyl chloride, polyethylene, butyl rubber, tar, asphalt, paints, polyurethane, and epoxy. To prevent, or minimize these effects, it has been common to treat wood with coatings that repel water, commonly referred to as water repellents, water proofers, and sealers and provide other barrier properties. These coatings can be film forming and/or penetrating coatings.
As stated above, a number of different types of coating materials have been used to impart water repellency to surfaces such as concrete, masonry products and wood. For the most part, they are either highly toxic or harmful to the environment, contain high organic solvent concentrations, are not as effective as is desired, are economically expensive, and/or must contain various additives to impart water repellency/hydrophobicity to the surface being coated. Also, such coatings may also seal the product completely, preventing or greatly reducing the escape of moisture from the coated substrate.
The following references are representative of the art with respect to methods and compositions for imparting weather resistance to porous substrates such as concrete, masonry and wood products.
U.S. Pat. No. 6,555,641 discloses waterborne wood coating formulations based upon water reducible alkyds and acrylic latex materials as a means to obtain a desirable level of water for repellency for wood products. Highly hydrophobic additives are included in the wood coating formulations.
U.S. Pat. No. 4,285,997 discloses a method for treating wood to enhance its properties. The method comprises contacting the wood to be treated with sufficient water dilutable acrylic resin formed from at least one vinyl monomer in a solvent consisting essentially of water to deposit an effective amount of said resin in the cell walls of said wood. The resin contains molecules having a molecular weight of less than about 1000 and of a size which can enter the free space of the cell walls and in an amount sufficient to stabilize the wood. The resin also has a minimum film forming temperature of not greater than ambient, and converts to a water insoluble form at ambient conditions in the cell walls.
U.S. Pat. No. 4,276,329 discloses a method for treating wood to enhance its properties comprising: contacting the wood to be treated with sufficient water dilutable resin in a water miscible solvent, the resins capable of being converted within the cell walls of the wood to a water insoluble form. Water dilutable alkyds and urethane modified alkyds are disclosed as preferred resins.
JP 2000-238011 A2 (Chemical Abstracts abstract) discloses a timber surface treatment by coating the timbers with polymer resin by immersing in an emulsion containing ≧1 selected from ethylene-vinyl acetate copolymer, poly(vinyl acetate), and acrylic styrene copolymer, to prevent the timbers from water penetration or evaporation.
U.S. Pat. No. 3,754,983 discloses wax polymer compositions suitable for imparting water resistance to paper, paperboard, or wood, designed for application at ≧200° F., consisting of a mixture of paraffin wax (m.p. 143–150° F.) 70–90, 5–30% by weight of an ethylene-vinyl acetate copolymer (Elvax 260) and a gel-forming agent, e.g., Al alkoxide, Sec-butoxyaluminum stearate, aluminum 2-ethylhexoxide, aluminum isopropoxide, or aluminum sec-butoxide (II), 1–5%.
U.S. Pat. No. 4,229,507 discloses a barrier coating for wood to prevent excessive drying and shrinkage on the surface of wood comprised of aqueous polymeric emulsions having a minimum film-forming temperature of not higher than 40° C. Examples include butadiene-styrene latexes, acrylics, synthetic rubbers, polyvinyl acetate, and ethylene vinyl acetate copolymers. Example 5 discloses a wood product coated with an ethylene-vinyl acetate copolymer having a minimum film-forming temperature of 10° C. (Sumica Flex 500).
U.S. Pat. No. 3,900,620 discloses aluminum systems as wood-stain reducing agents based upon water soluble aluminum halides. These halides can be incorporated as a single emulsion, with a latex emulsion or water base emulsion paints. The aqueous based emulsions include an acrylic latex, a polyvinyl acetate copolymer (UCAR 1251), a vinyl acrylics, and an alkyd.
U.S. Pat. No. 5,702,509 ('509) and U.S. Pat. No. 5,051,129 ('129) disclose water repellant compositions for treating masonry surfaces. The '509 patent discloses the use of hydrophobic moiety-containing compounds such as alkoxysilanes, alkoxysiloxanes and '129 discloses the use of water soluble coupling agent and an alkyltrialkoxysilane to provide barrier properties.